This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A230552 #13 Oct 28 2013 13:29:49 %S A230552 1,2,4,10,25,66,170,441,1124,2870,7273,18477,46825,118917,301734, %T A230552 766525,1946293,4944614,12557685 %N A230552 Number of involutions avoiding the pattern 2341. %H A230552 Miklós Bóna, Cheyne Homberger, Jay Pantone, and Vince Vatter, <a href="http://arxiv.org/abs/1310.7003">Pattern-avoiding involutions: exact and asymptotic enumeration</a>, arxiv:1310.7003, 2013. %e A230552 Of the 26 involutions of length 5, only 52341 contains the pattern 2341, so a(5) = 25. %Y A230552 Cf. A001006, A121704, A230551-A230556. %K A230552 nonn %O A230552 1,2 %A A230552 _Cheyne Homberger_, Oct 23 2013